No, because you do not need a voltage to maintain a magnetic field, the only time there needs to be a voltage across the magnet is when you are ramping up the field.
In fact, most high-field electromagnets are made from superconducting wire so once you have ramped up the field you can turn off the source.
Hence, the energy needed depends on propeties of the magnet you are using; although if you know the current an inductance you can of course just use LI^2/2 to calculate the energy stored in it.

That said, if you look at the NHMFL website you will see that their 45T magnet uses 33 MW of power (it is a hybrid magnet).

Staff: Mentor

With a non-superconducting coil you do need to apply some voltage in order to maintain the current, which is what produces the magnetic field. The voltage depends on the resistance of the coil and and the current through it via Ohm's Law.